The invention relates to a method of producing trench-like depressions in the surface of a wafer, particularly a silicon wafer or a glass wafer, by plasma etching, wherein the depressions are formed by alternate passivation and etching. The invention further relates to a micronozzle produced by the method and a nebuliser comprising a micronozzle.
For producing micronozzles for dispensing a fluid it is known to produce them from a composite of a silicon wafer and a glass plate applied thereto. In this process microporous structures or channels, which form nozzle channels in conjunction with the glass plate, are etched into the wafer surface. Alternatively, microporous structures or channels may be etched into the surface of a glass plate or a glass wafer to form nozzle channels in conjunction with a silicon wafer or another glass plate. By suitably cutting the composite consisting of silicon wafer and glass plate, micronozzles can then be cut from it by sawing. The micronozzle may comprise two or more plates, of which at least a first plate has a trench-like structure, the trenches connecting the inlet side and the nebuliser nozzle(s) provided as outlet(s) on the opposite side, while another, generally unstructured second plate is placed on the structured side of the first plate and fixedly attached thereto. A nozzle body comprising three layers may consist, for example, of a structured silicon plate, a planar silicon cover plate and a thin glass plate arranged between them.
According to DE 42 360 37 A1 a thin layer of silicon is thermally oxidised on the surface that is to be structured. The oxide layer subsequently serves as a mask for etching the trench structures. A photosensitive plastics layer is applied to this layer by centrifugation and bonded thereto. The structures are transferred into this plastics layer photo-optically by contact copying using a mask on a scale of 1:1 and developed. Alternatively, the structures may be transferred into the plastics layer by projection lithography using masks with preferably 5× magnified structures and developed. The plastics structures are used in the next process step as masking for the structuring of the silicon dioxide layer. This structuring is carried out by reactive etching with ion beams. During the structuring of the oxide layer, the plastics is removed entirely or removed after the oxide structuring or silicon structuring. The oxide layer structured in this way then acts as masking for etching the, for example, 5-7 μm deep trench structures in the silicon. At the same time the oxide layer is slowly removed. At the end of this structuring process, there are U-shaped or rectangular, box-shaped trench structures on the silicon plate, but in plan view these structures may have virtually any desired plane geometry. These etched shapes may be produced both by isotropic dry etching processes and also by isotropic wet etching processes. With anisotropically acting etching processes (both with reactive ion plasma and with wet-chemical agents) it is possible to obtain triangular nozzle cross-sections from V-shaped trench structures or trench structures with perpendicular edges of monocrystalline base plates. The geometric shapes of the trenches may also be altered by a combination of etching techniques and coating techniques. Virtually any desired geometric shapes may be obtained. After the structuring, the silicon plate is cleaned and the remaining silicon dioxide is removed by wet chemical methods.
Micronozzles of this kind are used, for example, in medical inhalers, the technical principles of which are described, for example, in WO 91/14468 or WO 97/12687. In these inhalers the amount of liquid medicament formulation to be nebulised is forced by high pressure up to 500 bar through a micronozzle with preferably two nozzle exits and thereby converted into the respirable aerosol. Reference is made expressly to the above-mentioned documents in their entirety, within the scope of the present description.